Well, you can always start with the eraser tool.
Zoom in to make it easier, using the [ and ] buttons to adjust the brush size easily/quickly.
Another way would be to use the line tool on a new layer around what you want, select using magic wand delete off the original layer.
If you post the image I could do it for you?

Your sig isn't using sig basics.
Obviously you are clearly trying for something different, but you still need to remember Focal point, flow, composition and depth.
The focal is hard to pick out because the text covers the whole sig, and therefore removes a clear focal. Remember (or google) the rule of thirds.
Example of a good Focal point. - notice where the main focal (face) is laced in the sig.
The flow is not terrible, but the text really ruins it. Remember that text needs to follow the flow just as a render or stock does.
Example of good flow. - all the effects flow in the same direction.
Composition in text sigs are hard. Try looking up some general typography tutorials (photoshop/gimp ones should be fine) to see how things are placed.
Example of good composition - Everything on the sig draws your eyes to the focal point, which is cleverly placed using the rule of thirds.
Depth. At the moment, it all looks very flat. Try making some of the wavy bit infront the text. Blur some background - some decent lighting always works well for me.
Example of good depth. - it looks very 3D, you can easily tell where the foreground, background and main areas all meet, yet are not flat.
[all sigs where made by me using paint.net, no ripping, thanks]

This can count right??
It is to do with astronomy, and also sciency stuff due to the wireframes.
Stocks:
http://img411.imageshack.us/img411/754/72137836.png
http://img709.imageshack.us/img709/5691/34780599.jpg
We edited in the sparkles as soon as we took it, so I don't actually havee the original stock, but that is the picture we took in it's closest to original form

Thats not fail. When you smudge it, go over the back of the render more so it looks like he is walking out the Background. That will blend it.
With the dots over the top, they need to vary in darkness (which I didn't to) which is easy to do.
Dup the background layer and put it under the dots. Selects all the dots (magic wand global) the then go onto the Duped layer and Ctrl I to invert selection. Then hit delete. Remove the dots layer.

You get the nice lighting effects by doing the last step
Make a new layer and select paintbrush tool. Draw red colour dots everywhere at any size.
Select them all using Magicwand on global setting.
Run nebulous at default settings.
effect-blur-zoom zoom blur. Move blur amount to full and select where you want the light to come from. I choose on the left hand side. Press ctrl F twice, maybe more depending on how big your image is and how many dots you did. The more times you run it the more light.
Whack that layer on colour dodge at 240.

This is what we will be making
You will need the
Smudge plug-in.
And curves+
Nebulous
Follow this tutorial for the background cloudy effect. I didn't use this but it gives the exact same effect and is a lot easier and faster. Make sure you don't make it too dark. I did and if you do just use adjustments-lighten until it looks like my starting image.
Open up your render. I used this but it should work with most renders. Paste it onto a new layer above the background.
Dup the Background and move the layer to the top. Go to the layer with the render and select the render using the magic wand (you can select around the render and press ctrl I to invert). Delete this selection from the second Background layer.
Not go to effects-distort-smudge and use the paint brush. Twist it over the edge of the render. Don't cover to much up. Dup the layer and set the top one to overlay.
Now dup the render 5 times and move these 5 to the top.
From bottom to top (not including original) do this.
1. gaussian blur 7 px and set layer a addictive.
2. Motion blur at 20 pixels (the angle changes on which way you want the render to come from.) and untick centered.
3. Leave how it is.
4. Set layer mode to lighten
5. Adjustments-black and white - lower opacity to about 180 - set to multiply. You may need to adjustments-lighten this layer.
Now for more smudging. Dup the bottom layer. Erase over render. Smudge (use paintbrush) over back of render (so if it is coming from left smudge over the left) and erase anything not smudged.
Set to overlay. This makes it look like it is coming out of the background and tints the colour.
Make a new layer and select paintbrush tool. Draw red colour dots everywhere at any size.
Select them all using Magicwand on global setting.
Run nebulous at default settings.
effect-blur-zoom zoom blur. Move blur amount to full and select where you want the light to come from. I choose on the left hand side. Press ctrl F twice, maybe more depending on how big your image is and how many dots you did. The more times you run it the more light.
Whack that layer on colour dodge at 240.
Tadda. That should do it.
Extras:
Add a border. Just draw around the edge in black.
Dirt. Using the splatter plug-in (no line width and about 3 on splat size) or paintbrush. Blur down at about 3-6 pixels.
Colour: If it is looking a bit dull brighten it up by adding a gradient on an overlay layer.
It turns out like this.
Post your outcomes
I have attached the render I used.
OUTCOMES:

Made this, trying out an old style in a new way.
I re-coloured the one above a few times so it matched a kuler scheme and I think this one turned out the best.
A simple street fighter 2 sig. I have been addicted to this for years, I still have a working snes and play on this every day, even though I am only 12.
People on this sit seem to like text sigs so I made a quick one and entered it in a life inspiration contest on kong.

Kinda yeah. I made it first without and it seemed empty. I didn't want to change the compo cuz I would have to change everything else so I just added some hexagons. Surprisingly they work for most pieces, not just the bumble bee one.

Kinda yeah. I made it first without and it seemed empty. I didn't want to change the compo cuz I would have to change everything else so I just added some hexagons. Surprisingly they work for most pieces, not just the bumble bee one.